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WO2025215696A1 - Dispositif d'évaluation de caractéristique optique et procédé d'évaluation de caractéristique optique - Google Patents

Dispositif d'évaluation de caractéristique optique et procédé d'évaluation de caractéristique optique

Info

Publication number
WO2025215696A1
WO2025215696A1 PCT/JP2024/014244 JP2024014244W WO2025215696A1 WO 2025215696 A1 WO2025215696 A1 WO 2025215696A1 JP 2024014244 W JP2024014244 W JP 2024014244W WO 2025215696 A1 WO2025215696 A1 WO 2025215696A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical fiber
core
mode
dependent loss
waveform
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2024/014244
Other languages
English (en)
Japanese (ja)
Inventor
惇平 早川
篤志 中村
優介 古敷谷
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NTT Inc
NTT Inc USA
Original Assignee
Nippon Telegraph and Telephone Corp
NTT Inc USA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Telegraph and Telephone Corp, NTT Inc USA filed Critical Nippon Telegraph and Telephone Corp
Priority to PCT/JP2024/014244 priority Critical patent/WO2025215696A1/fr
Publication of WO2025215696A1 publication Critical patent/WO2025215696A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties

Definitions

  • This disclosure relates to an apparatus and method for evaluating the mode-dependent loss of a coupled multi-core optical fiber.
  • a multi-core optical fiber is an optical fiber that has multiple cores in a single strand. In comparison with conventional fibers, conventional fibers have only one core. Because the number of cores increases, multi-core optical fibers have the advantage of increasing the communication capacity per optical fiber.
  • multi-core optical fibers are divided into uncoupled and coupled types.
  • Uncoupled types are those in which the cores of a multi-core optical fiber are separated by a large distance, and each core is treated as an independent entity.
  • coupled types are those in which the cores of a multi-core optical fiber are not separated by a large distance, and some of the communication light propagating through one core is actively coupled to adjacent cores.
  • a coupled multi-core optical fiber can accommodate a larger number of cores per optical fiber than an uncoupled multi-core optical fiber. This means that the communication capacity per optical fiber can be increased. Therefore, coupled multi-core optical fiber is one of the optical fibers that holds promise as a medium for realizing large-capacity optical communications in the future.
  • MDL mode-dependent loss
  • Mode-dependent loss is considered a parameter that limits transmission capacity, and is known to be highly dependent on bending of coupled multi-core optical fibers and core misalignment during splicing.
  • mode-dependent loss changes due to bending of coupled multi-core optical fibers and poor splicing that occurs during construction of the transmission line. Therefore, it is necessary to evaluate the mode-dependent loss of coupled multi-core optical fibers when constructing a transmission line.
  • Figure 1 is a diagram explaining coupled multi-core optical fibers and mode-dependent loss. Take as an example a coupled multi-core optical fiber 50 with two cores (core C1 and core C2). As shown in Figure 1(A), the two cores are parallel, and light propagating to core C1 moves from core C1 to core C2, and then from core C2 to core C1. This transition of light across cores is called mode coupling, and an optical fiber in which the cores are coupled at any location is called a coupled multi-core optical fiber.
  • Figure 1(B) is a diagram explaining mode-dependent loss. It considers loss per segment. For example, let's say the loss in segment S1 of core C1 is 1 (shown as "-1" on the diagram). Light propagating through core C1 then moves from core C1 to core C2, losing 1 in each of segments S2 and S3. Therefore, light passing through three segments (segment S1 to core C1, segment S2 to core C2, segment S3 to core C2) loses a total of 3. Similarly, light propagating through core 2 loses a total of 7 in three segments (segment S1 to core C2, segment S2 to core C1, segment S3 to core C1). Note that the path taken (including transitions between core C1 and core C2) is determined by the state (amplitude and phase) of the incident light on each core. In other words, mode-dependent loss can be said to be the difference in loss depending on the path light has traveled.
  • Non-Patent Documents 1 and 2 disclose methods for evaluating mode-dependent loss.
  • Non-Patent Document 1 discloses a method for measuring mode-dependent loss from the amplitude and phase information of the propagating light output from the optical fiber under test.
  • Non-Patent Document 2 proposes a method for evaluating mode-dependent loss from changes in the intensity of light output from the optical fiber under test by randomly changing the intensity and phase state of the light input to the optical fiber under test.
  • Fontaine, N. K. , et al. “Characterization of Space-Division Multiplexing Systems using a Swept-Wavelength Interferometer”. Optical Fiber Communication Conference/National Fiber Optic Engineers Conference 2013. OW1K. 2, 2013. Hasegawa, T. and T. Hayashi. “Measurement of Mode Dependent Loss of Randomly-Coupled Multi-Core Fiber usin g Scrambling Method”, T2C, in 26th Optoelectronics and Communications Conference. 2021.
  • both ends of the optical fiber under test are located at separate locations.
  • the present invention aims to provide an optical characteristic evaluation device and an optical characteristic evaluation method that can evaluate mode-dependent loss from one end of an optical fiber under test.
  • the optical characteristic evaluation device of the present invention evaluates mode-dependent loss by utilizing backscattered light from an optical pulse input from one end of the optical fiber under test.
  • the optical characteristic evaluation apparatus is an optical characteristic evaluation apparatus including an optical time domain tester and an analysis unit
  • the optical time domain tester comprises: a test optical pulse is input to one core of a multi-core optical fiber at one end of the multi-core optical fiber as an optical fiber to be tested, and backscattered light output from the core is received; and a waveform of the light intensity of the backscattered light with respect to a distance of the multi-core optical fiber is obtained,
  • the analysis unit performing a linear approximation on a desired section of the waveform; calculating dispersion for the linear approximation of the waveform in the desired section; and using the dispersion as an evaluation value of mode-dependent loss for the multi-core optical fiber.
  • an optical characteristic evaluation method is an evaluation method for evaluating a mode dependent loss of a multi-core optical fiber that is an optical fiber under test, the method comprising the steps of: connecting an optical time domain tester to one end of the multi-core optical fiber; injecting a test optical pulse into one of the cores of the multi-core optical fiber; receiving backscattered light output from the core; acquiring a waveform of the light intensity of the backscattered light with respect to the distance of the multi-core optical fiber; performing a linear approximation on a desired section of the waveform; calculating dispersion for the linear approximation of the waveform in the desired section; and using the dispersion as an evaluation value of mode-dependent loss for the multi-core optical fiber.
  • the backscattered light of an optical pulse incident on an optical fiber has various states (phase/amplitude).
  • the backscattered light then returns to the input end of the optical pulse.
  • This backscattered light it is possible to evaluate the mode-dependent loss at one end of a coupled multi-core optical fiber.
  • the intensity of backscattered light that passes through a segment in which mode-dependent loss (difference in loss between cores) occurs changes depending on the core through which it passes within that segment, resulting in a large difference (variation) in the intensity of the backscattered light.
  • the difference (variation) in the intensity of the backscattered light is small, it is backscattered light that occurred when the test light pulse passed through a segment with no (or small) mode-dependent loss, and if the difference (variation) in the intensity of the backscattered light is large, it can be said to be backscattered light that occurred when the test light pulse passed through a segment with (or large) mode-dependent loss.
  • mode-dependent loss can be evaluated by performing a linear approximation on the waveform of the backscattered light and calculating the variance of the waveform relative to that approximate straight line.
  • the present invention can provide an optical characteristic evaluation device and optical characteristic evaluation method that can evaluate mode-dependent loss from one end of the optical fiber under test.
  • the analysis unit determines the position where the dispersion changes as the position where mode-dependent loss occurs.
  • the present invention provides an optical characteristic evaluation device and optical characteristic evaluation method that can evaluate mode-dependent loss from one end of an optical fiber under test.
  • 1A and 1B are diagrams illustrating a coupled multi-core optical fiber and mode-dependent loss.
  • 1A and 1B are diagrams illustrating a conventional coupled multi-core optical fiber and a method for evaluating mode-dependent loss.
  • 1 is a diagram illustrating an optical property evaluation apparatus according to the present invention.
  • 1A to 1C are diagrams illustrating an optical property evaluation method according to the present invention.
  • 1A to 1C are diagrams illustrating an optical property evaluation method according to the present invention.
  • FIG. 1 is a diagram illustrating a method for evaluating mode-dependent loss.
  • 1 is a diagram illustrating the difference between a conventional method and the method of the present invention for evaluating mode-dependent loss.
  • 10A and 10B are diagrams illustrating waveforms of backscattered light obtained in evaluation of mode-dependent loss.
  • 5A and 5B are diagrams illustrating information displayed on a display unit of the optical property evaluation apparatus according to the present invention.
  • the optical characteristic evaluation apparatus 301 includes an optical time domain tester 10 and an analysis unit 20.
  • the optical pulse tester 10 includes: At one end of the multi-core optical fiber 50, which is the optical fiber under test, a test optical pulse is input into one of the cores of the multi-core optical fiber 50, and backscattered light output from the core is received; and a waveform of the light intensity of the backscattered light with respect to the distance of the multi-core optical fiber 50 is obtained.
  • the analysis unit 20 performing a linear approximation on a desired section of the waveform;
  • the dispersion for the linear approximation of the waveform in the desired section is calculated; and the dispersion is used as an evaluation value of the mode-dependent loss for the multi-core optical fiber.
  • the optical pulse tester 10 includes a pulse light source unit 11, an input/output unit 12, and a receiving unit 13.
  • the pulse light source unit 11 outputs a test optical pulse to be incident on the optical fiber under test.
  • the input/output unit 12 includes, for example, an optical circulator 12a and an input/output device 12b.
  • the receiving unit 13 includes, for example, an opto-electrical converter 13a and an AD converter 13b.
  • the analysis unit 20 includes a waveform analysis unit 21, a mode-dependent loss evaluation unit 22, and a display unit 23.
  • FIG. 4 is a diagram illustrating the operation of the optical property evaluation device 301.
  • the optical characteristic evaluation device 301 connecting the optical time domain tester (10) to one end of the multi-core optical fiber (50);
  • a test optical pulse is input from the optical pulse tester 10 to one of the cores of the multi-core optical fiber 50 (step St01); receiving backscattered light output from the core with an optical time domain tester (10) (step St02);
  • the analysis unit 20 acquires a waveform of the light intensity of the backscattered light with respect to the distance of the multi-core optical fiber 50 (step St03); performing linear approximation on a desired section of the waveform in an analysis unit; calculating a variance of the linear approximation of the waveform in the desired section by an analysis unit;
  • the analysis unit 20 uses the dispersion as an evaluation value of the mode-dependent loss for the multi-core optical fiber (step St04), and the display unit 23 displays the evaluation value (step St05). It is characterized by:
  • step St00 the input/output unit 12 of the optical time domain tester 10 is connected to one end of the multi-core optical fiber 50.
  • step St01 a test optical pulse is generated by the pulse light source 11, and the test optical pulse is incident on an arbitrary core at one end of the multi-core optical fiber 50 via the input/output unit 12, thereby generating backscattered light within the multi-core optical fiber 50.
  • step St02 the backscattered light output from an arbitrary core at one end of the multi-core optical fiber 50 is sent to the receiving unit 13 via the input/output unit 12.
  • the photoelectric converter 13a of the receiving unit 13 converts the backscattered light intensity into an electric signal
  • the AD converter 13b converts it into a digital signal and sends it to the analyzing unit 20.
  • the waveform analyzer 21 of the analyzer 20 acquires the backscattered light intensity waveform with respect to the distance from one end of the multi-core optical fiber 50 from the received light signal.
  • the mode-dependent loss evaluation unit 22 of the analysis unit 20 analyzes and evaluates the backscattered light intensity waveform. Details of the evaluation method will be described later.
  • step St05 the evaluation value obtained by the mode-dependent loss evaluation unit 22 is displayed on the display unit 23.
  • Figure 5 is a diagram explaining this optical characteristic evaluation method. The explanation will be given assuming that the optical fiber under test is a two-core coupled multi-core fiber 50, but the same applies if the multi-core fiber 50 has three or more cores.
  • test optical pulse generated by the pulse light source 11 is input into any one core of the multi-core fiber 50 via the optical circulator 12a and the input/output device 12b. For example, let's assume that the test optical pulse is input into core C1.
  • the test optical pulse propagates through the multi-core optical fiber 50, and during this propagation process it couples with another core C2. Assume that there is a region 50X at an arbitrary location in the multi-core optical fiber 50 where the difference in loss between cores is large (large mode-dependent loss). In region 50X, there is a difference in loss between core C1 and core C2 (large loss in core C1, small loss in core C2) (see Figure 5(A)).
  • the test light pulse is scattered as it propagates through the optical fiber under test, with a portion returning to the side where the test light pulse is incident. This returning light is called backscattered light.
  • the measurement target is the backscattered light intensity of a single core (core C1).
  • the backscattered light is converted into a digital signal by photoelectric converter 13a and AD converter 13b via input/output device 12b and optical circulator 12a.
  • the waveform analysis unit 21 acquires the relationship between the distance of the optical fiber under test and the backscattered light intensity (OTDR waveform).
  • Figure 5(B) shows an OTDR waveform with the horizontal axis representing distance and the vertical axis representing backscattered light intensity.
  • This OTDR waveform has two sections: one with small variation and one with large variation. It is believed that differences in mode-dependent loss occur where the variation in the OTDR waveform changes (including steps). In other words, the magnitude of the difference in mode-dependent loss is evaluated from the magnitude of the change in variation in the OTDR waveform.
  • the location can be identified from the horizontal axis. Specifically, as shown in I-2 in Figure 5(B), the location where the variation changes is considered to be the MDL occurrence point (location of area 50X).
  • Figure 6 is a diagram explaining a method for evaluating mode-dependent loss. By randomly changing the state of the incident light, all manner of mode-coupled states can be generated, and the magnitude of mode-dependent loss can be evaluated from the variation in the intensity of the light (output light) that passes through the core.
  • Figure 6(A) is a diagram explaining the case where light is concentrated on the path Rs, which has low loss.
  • Figure 6(B) is a diagram explaining the case where light is concentrated on the path Rl, which has high loss.
  • Figure 6(C) is a diagram explaining the change in the light intensity of the output light when the difference in mode-dependent loss is large.
  • Figure 6(D) is a diagram explaining the change in the light intensity of the output light when the difference in mode-dependent loss is small.
  • Figure 7 is a diagram explaining the difference between the conventional method and the method of the present invention for evaluating mode-dependent loss.
  • Figure 7(A) is a diagram explaining the conventional method.
  • test light is generated by giving random phase and amplitude to light from a light source 31 using an optical modulator 32. The test light is then incident on one end of a multi-core optical fiber 50, passes through the multi-core optical fiber 50, and is received by a light-receiving device 33 located at the other end, obtaining a waveform such as that described in Figure 6. For this reason, it is necessary to position workers at both ends of the multi-core optical fiber 50.
  • Figure 7(B) is a diagram explaining the technique of the present invention.
  • the test light pulse input into the multi-core optical fiber 50 is scattered at each point in the multi-core optical fiber 50, and a portion of it returns as backscattered light.
  • the backscattered light has a random phase and amplitude. For this reason, it is possible to evaluate the mode-dependent loss without modulating the light on the side where the test light is input, and because the backscattered light that returns to the input side of the test light is used, the mode-dependent loss can be evaluated at the input end of the test light.
  • FIG. 8 is a diagram illustrating the waveform of backscattered light obtained in the evaluation of mode-dependent loss.
  • the backscattered light at each point in the coupled multi-core optical fiber has a random optical state (phase and amplitude).
  • the mode coupling state in the coupled multi-core optical fiber varies depending on the phase difference of the light propagating through the multiple cores. Therefore, the backscattered light generated at each point (generated beyond the target position of the multi-core optical fiber 50) randomly changes the mode coupling state at the target position.
  • Figure 8 shows the backscattered light intensity waveform that passes through the target position and returns to the input end of the test light.
  • a linear approximation is performed on the backscattered light intensity waveform in Figure 8 (linear approximation line I-7), and the variance of the backscattered light intensity waveform relative to linear approximation line I-7 is used as the evaluation value for mode-dependent loss. If the variance is large, it can be evaluated that the difference in mode-dependent loss at the point of interest is large.
  • Figure 9 is a diagram explaining the information displayed on the display unit 23.
  • the display unit 23 displays the acquired backscattered light intensity waveform.
  • the operator sets the range I-9 for calculating the mode-dependent loss evaluation value.
  • the mode-dependent loss evaluation unit 22 performs a linear approximation of range I-9, calculates the variance within the same range, and displays the variance on the display unit 23 (I-10).
  • the magnitude of the mode-dependent loss of a coupled multi-core optical fiber can be easily evaluated by measuring it at one end of the optical fiber. By repeating such measurements, a high-quality network can be constructed and high-quality services can be provided to users.
  • Mode-dependent loss The loss ratio between the core with the highest loss and the core with the lowest loss among the cores in a multi-core optical fiber.
  • PM in the optical modulation unit 32 in FIG. 7 Phase modulator PM connected to the far end of the multi-core optical fiber 50 in FIG. 7: Power meter
  • Optical pulse tester 11 Pulse light source 12: Input/output unit 12a: Optical circulator 12b: Input/output device 13: Receiver 13a: Photoelectric converter 13b: AD converter 20: Analyzer 21: Waveform analyzer 22: Mode-dependent loss evaluation unit 23: Display 31: Light source (tunable wavelength light source) 32: Modulation unit 33: Light receiving device (power meter) 50: Multi-core optical fiber 50X: Region 301: Optical characteristic evaluation device

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Testing Of Optical Devices Or Fibers (AREA)

Abstract

Le but de la présente invention est de fournir un dispositif d'évaluation de caractéristique optique et un procédé d'évaluation de caractéristique optique qui permettent d'évaluer une perte dépendant du mode à partir d'une extrémité d'une fibre optique soumise à un test. Un dispositif d'évaluation de caractéristique optique (301) selon la présente invention est pourvu d'un testeur d'impulsions optiques (10) et d'une unité d'analyse (20).　Le testeur d'impulsions optiques (10) est caractérisé par : l'introduction, à une extrémité d'une fibre optique multicœur (50) qui est soumise à un test, d'une impulsion de lumière de test à l'un des cœurs de la fibre optique multicœur (50), et la réception d'une lumière rétrodiffusée émise par le cœur ; et l'acquisition de la forme d'onde de l'intensité de la lumière rétrodiffusée par rapport à la distance de la fibre optique multicœur (50). L'unité d'analyse (20) est caractérisée par : la réalisation d'une approximation linéaire sur une section souhaitée de la forme d'onde ; le calcul de la variance de la forme d'onde dans la section souhaitée par rapport à l'approximation linéaire ; et la prise en compte de la variance en tant que valeur d'évaluation de la perte dépendant du mode de la fibre optique multicœur (50).
PCT/JP2024/014244 2024-04-08 2024-04-08 Dispositif d'évaluation de caractéristique optique et procédé d'évaluation de caractéristique optique Pending WO2025215696A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/JP2024/014244 WO2025215696A1 (fr) 2024-04-08 2024-04-08 Dispositif d'évaluation de caractéristique optique et procédé d'évaluation de caractéristique optique

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2024/014244 WO2025215696A1 (fr) 2024-04-08 2024-04-08 Dispositif d'évaluation de caractéristique optique et procédé d'évaluation de caractéristique optique

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WO2025215696A1 true WO2025215696A1 (fr) 2025-10-16

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PCT/JP2024/014244 Pending WO2025215696A1 (fr) 2024-04-08 2024-04-08 Dispositif d'évaluation de caractéristique optique et procédé d'évaluation de caractéristique optique

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